Because of widespread use of satellite positioning systems by stationary and mobile communications systems that include mobile terminals, such as cellular telephones, “spoofing,” the use of counterfeit positioning signals to provide a false location to a device, is of growing concern.
The Global Positioning System (GPS) is owned and operated by the U.S. Department of Defense, but is available for general use around the world. Other satellite positioning systems are also in use including but not limited to Glonass and Gallileo. Collectively, these and other similar systems are referred to in this document as satellite positioning systems (SPS). Briefly, SPS includes functioning satellites and back-up satellites that orbit above the Earth. SPS satellites continually broadcast their position and time. On earth, each SPS receiver, (collectively, “receiver” in this document) may contain a processor capable of trilaterating or multilaterating its own position through the use of SPS signals.
Positioning systems often augment traditional SPS signal sources through the use of signals from wireless base stations and other terrestrial transceivers. These base station signals can be used either as incremental location signals or as replacement signals to calculate the location of the receiver. Similar to SPS technology, the base station signals can be used to trilaterate or multilaterate the location the location of the mobile terminal independently of, or in conjunction with, SPS signal sources. Multiple functionalities now are prevalent in personal portable and/or mobile wireless communications instruments such as mobile terminals. It is now common for a mobile terminal to include a satellite positioning system receiver (in this document, an “SPS receiver”). A device containing an SPS receiver also includes a power supply system. The power supply system includes at least one battery and may include an alternative external power connector for connecting a mobile terminal to an external power source. A device containing an SPS receiver also may include at least one processor and at least one storage medium, such as random access memory (RAM) and FLASH memory (in this document, “memory”). In the case of a mobile terminal, the device also includes a wireless communications transceiver (in this document, a “wireless transceiver”). As indicated in the “Definitions” provisions of this document, a variety of satellite positioning systems, mobile terminals, communication networks including mobile wireless communication systems, and/or position determination systems may be used to facilitate implementation of the anti-spoofing detection system disclosed in this document.
It is apparent, therefore, in view of the reliance on SPS by many people and institutions, that spoofing of location information signals to create a false location calculation is not only unacceptable, but may dramatically affect commercial and national interests.
One way to degrade use of an SPS system is to jam it. Simply jamming an SPS is annoying, but is less consequential because the victim may be alerted to jamming, and/or the location calculation may be completed utilizing other signal sources, such as wireless communication system signals. Undetected spoofing, may result, however, in the use of a false location. The target of spoofing may be unaware that signals received are, in fact, counterfeit or inauthentic. Thus, the spoofed signals may be used in a position calculation that will impact actions dependent on an accurate location, such as navigation and tracking. Detecting such a spoofed signal and its resulting incorrect location information is, therefore, critical.
As regards the process of spoofing, one method includes a counterfeit or inauthentic signal source broadcasting counterfeit location signals at a higher power level than the actual location signals, possibly in conjunction with blockage or attenuation of the actual signals.
Determination of the location of the mobile terminal through the use of terrestrial communications signals generally requires identification of visible base transceiver stations, location of the base transceiver stations, and timing information to determine signal delay or signal strength between each base transceiver station and the wireless mobile transceiver. These methods are known in the art. In general, because the communication system must not only provide signals for location, but also for communications purposes, base transceiver station signals are more difficult and less likely to be spoofed than SPS signals, which generally are unidirectional.
Detecting such a spoofed signal and its consequent incorrect location information therefore is important. At least the following rely on one or more SPS's to function properly: truckers and truck dispatchers, power stations, air traffic control centers, banks and other financial institutions and police. A broad array of location-based services, such as asset tracking and theft prevention, felon tracking, geographic information system (GIS) resource lookup and child locators also depend on accurate SPS location.
When a mobile terminal operatively connectable to an SPS is powered on, it may establish a communication link with a base transceiver station. The mobile terminal will typically receive pilot signals from multiple base transceiver stations. The mobile terminal will search for signals from these base transceiver stations to establish a communication link with a selected base transceiver station to permit the reception and transmission of data over the established communication link. Transmitter or transceiver location information references, generally called “almanacs,” include transceiver identification information for base transceiver stations and transceiver location information.